<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    input[type="text"] {
      width: attr(maxlength em);
    }
    p::before {
      content: attr(id);
    }
  </style>
</head>
<body>
  <p id="sss">dddd</p>
  <input type="text" maxlength="10">
</body>
</html>